Until now, cemented carbides have been widely used as cemented carbide materials for use in grinding and cutting tools (e.g. drills, end mills, hobs, milling cutters, lathes, and pinion type cutters) and the like. Cemented carbide is an alloy formed by sintering hard metal carbide powders.
There is tungsten carbide as one of the cemented carbides. The tungsten carbide excels in heat resistance and chemical stability in addition to the property of high hardness. Therefore, the tungsten carbide has been used as a representative material for cemented carbide tools for many years. The cemented carbide tools are ones utilizing the cemented carbide. Heretofore, the cemented carbide tools have been widely used in metalworking for parts such as engine parts, transmission parts and stirring parts for automobiles.
However, the materials such as carbon fiber composite materials have been recently come into use in airframes and the like, and some of the carbon fiber composite materials have higher hardness than the conventional materials. Thus, when treating such materials with the tool made of the tungsten carbide, there were some instances where this tool was severely worn away to cause disruption. Accordingly, the developments of the cemented carbide materials having higher hardness than the tungsten carbide have been desired.
On the other hand, from the studies based on the theoretical calculations, hexagonal tungsten nitrides are predicted to be high hardness materials comparable to or exceeding the tungsten carbide (Non Patent Literature 1). Accordingly, the hexagonal tungsten nitrides are expected as the next generation cemented carbide materials.
The hexagonal tungsten nitrides include various structures such as h-W2N3 and δ-WN. For example, the K0 of h-W2N3 is 331 GPa and the K0 of δ-WN is 396 GPa, and thus the both structures are very hard (Non Patent Literature 2). The K0 means a volume modulus.
Very recently, a success in the synthesis of the hexagonal tungsten nitride having the h-W2N3 structure was reported in a literature (Non Patent Literature 2).
In this literature, however, only a small amount of the hexagonal tungsten nitride having the h-W2N3 structure was obtained as a by-product, which was mixed in other crystal phases. In short, the method described in this literature has been far from practical use as the method for synthesizing the hexagonal tungsten carbide having the h-W2N3 structure.